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Cold seep communities discovered at three previously unknown sites between 600 and 1000 m in Monterey Bay, California, are dominated by chemoautotrophic bacteria (Beggiatoa sp.) and vesicomyid clams (5 sp.). Other seep-associated fauna included galatheid crabs (Munidopsis sp.), vestimentiferan worms (Lamellibrachia barhami?), solemyid clams (Solemya sp.), columbellid snails (Mitrella permodesta, Amphissa sp.), and pyropeltid limpets (Pyropelta sp.). More than 50 species of regional (i.e. non-seep) benthic fauna were also observed at seeps. Ratios of stable carbon isotopes (δ13C) in clam tissues near -36‰ indicate sulfur-oxidizing chemosynthetic production, rather than non-seep food sources, as their principal trophic pathway. The 'Mt Crushmore' cold seep site is located in a vertically faulted and fractured region of the Pliocene Purisima Formation along the walls of Monterey Canyon (~635 m), where seepage appears to derive from sulfide-rich fluids within the Purisima Formation. The 'Clam Field' cold seep site, also in Monterey Canyon (~900 m) is located near outcrops in the hydrocarbon-bearing Monterey Formation. Chemosynthetic communities were also found at an accretionary-like prism on the continental slope near 1000 m depth (Clam Flat site). Fluid flow at the 'Clam Flat' site is thought to represent dewatering of accretionary sediments by tectonic compression, or hydrocarbon formation at depth, or both. Sulfide levels in pore waters were low at Mt Crushmore (ca 0.2 mM), and high at the two deeper sites (ca 7.011.0 mM). Methane was not detected at the Mt Crushmore site, but ranged from 0.06 to 2.0 mM at the other sites., Cited By (since 1996):108,
Invertebrates, CODEN: DRORE, ,

The validity of using morphological characteristics as predictors of age in the kelp, Pterygophora californica (Laminariales, Phaeophyta),

Description

Previous studies have used stipe ring counts to estimate the age of several species in the
Laminariales. Although this method is widely accepted, it has rarely been validated. To test the validity
of aging Pterygophora californica by counting rings formed in the stipe, we sampled plants of known
age between 1.0 and 4.4 yr old and plants with a calculated age of 12 yr. For a given cohort, the number
of complete rings closely approximated the known age in years. indicating ring counts are a reliable
method for estimating the age structure of P califomica populations. However, ring counts from
individual plants of known age can vary by ± 2 yr (95 % CI), and among readers counting the same
plants by ± 1 yr (95 % CI). Single plants, there fore, could not be reliably aged by ring counts Linear
relationships between 2 morphometric measures (stipe length and stipe diameter) and number of rings
varied both within and between stands and sites, suggesting these measures are not reliable for
estimating the age of this alga in the areas sampled. Stand density may be an important factor
contributing to the variation in these morphome tric measures. Short-term (22 wk) field manipulations of
stand density showed that plants at high density (30 plants m^-2) grew faster in stipe length and slower in
stipe diameter than those at medium (6 plants m^-2) and low (2 plants m^-2) densities. Plants collected in a multi-site survey, however, showed no relationship between stand density and stipe morphology,
indicating factors other than density also influence stipe growth Short-term (22 wk) field manipulations,
which reduced ambient light levels by up to 58 %. had no significant effects on stipe morphology., , ,

Remotely operated vehicle (ROV)-based mapping of tectonic features, zones of anomalous reflectivity, and geomorphic targets in Monterey Bay, California, demonstrates the regional abundance of fluid expulsion along the active transform margin between the Pacific and North American plates. Cold seeps - extant communities characterized by chemosynthetic bivalves, bacterial mats, and rare tubeworms - are the surface manifestations of present-day fluid expulsion of sulfide- and methane-rich fluids, whereas slabs, veins, and chimneys of authigenic carbonate represent regions of either dormant methane-rich fluid expulsion, or areas where the present rate of flow is too low to support chemosynthetic fauna. We have found both active and dormant fluid seepage along fault zones, at the surface expression of mud volcanoes, on organic-rich or permeable substrate, and within headless canyons across a wide range of depths within Monterey Bay. The fluid egress at these sites may be driven by a combination of (1) pore-space reduction caused by rapid sedimentation and/or tectonic compaction related to residual Pacific-North America compression, and (2) increased buoyancy due to a decrease in pore-fluid density related to diagenesis and/or catagenesis at depth. Although provocative, the relationship between topographically driven aquifer discharge and sea-floor fluid expulsion remains speculative for Monterey Bay. The widespread distribution of fluid expulsion features controlled by a variety of conduits in Monterey Bay implies that cold seeps may be common features on translational margins., Cited By (since 1996):60, CODEN: BUGMA, ,